1. Field of the Invention
This invention relates to a power split transmission of a traction drive of a vehicle, the power split transmission having a continuously variable transmission and a summing transmission. The continuously variable transmission has a primary unit and a secondary unit driven by the primary unit in both directions of rotation. The primary unit of the continuously variable transmission is driven by a drive motor, such as an internal combustion engine, of the vehicle. The primary unit is connected to a first drive element of the summing transmission, which summing transmission is in the form of a planetary transmission. The secondary unit of the continuously variable transmission is connected to a second drive element of the summing transmission. An output element of the summing transmission is in a driving connection with a wheel drive.
2. Description of Related Art
To comply with increasingly stringent exhaust standards and regulations, traction drives with power split transmissions that have a continuously variable gear ratio are being used to an increasing extent. Power split transmissions with a continuously variable gear ratio make it possible to achieve optimum efficiency in all operating ranges of the vehicle, which makes possible the more fuel-efficient operation of the drive motor of the vehicle, typically an internal combustion engine.
A traction drive with a power split transmission is described in EP 2 034 221 A2. Known power split transmissions have switchable clutch devices, such as wet multiple plate clutches or friction clutches, which co-rotate continuously during the operation of the power split transmission. The co-rotating clutch devices, on account of churning losses, reduce the efficiency of the traction drive. On account of an increased number of components, existing clutch devices of the power split transmission also require additional construction space and additional manufacturing effort and expense and increase the weight of the power split transmission.
Therefore, it is an object of this invention to provide a power split transmission of the general type described above but which represents an improvement in terms of its compact size, lighter weight, and greater efficiency.